Purification of hydrocarbon oils



@en 27, 1936. J. A. REID Er AL.

PURIFICATION OF HYDROCARBON OILS Filed June 1'?, 1935 Sl'lON'TiIW Nl `lVLLNlLOd NOILVGIXO KMCJ mma mQOJIU 05.050 mm ovm A TTORNEYS.

Patented Oct'. 27, 1936l 2,058,720 y rUamcArIoN or maooAnnoN ons James A. Reid and Walter A. Schulze, Bartlest f ville, Okla., assignors to Phillips Petroleum Company, Bartlesville, Okla., a corporation of Delaware Application June 11.7, 1935, Sal No; 27,109 5 en. (ci. 10e- 30) invention relates to improvements in processes for sweetening petroleum distillates by means of copper halides.

More speciiically it relates to the conduct of processes for sweetening mercaptan-bearing petroleum oil with a solution of a copper salt and a soluble chloride in a readily controllable manner, yielding under all circumstances a doctor sweet and otherwise satisfactory product of good stability as to color and other characteristics.

The sweetening of gasolines with copper halides has been described in the prior art. The process involves the conversion of mercaptans in the oil to disuldes with simultaneous conversion of the copper from the cupric to the cuprous state, the cuprous copper being regenerated to the cupric condition by aeration. In practicing the process, and especially when sweetening gasolines containing unsaturated compounds, it has often been diilicult or impossible to produce a product with suilicient color and gum stability; the instability is apparently the result. oi certain undesirable side reactions. l

Since we have discovered that this diftloulty may be overcome by controlling the reactivity of the copper solution during the operation of the process, a particular object of our invention'is a means for measuring the reactivity of such copper treating solutions.

We have found that the sweetening power or reactivity of a copper halide sweetening solution' meant the potential developed between a polished platinum or gold electrode and a" saturated calomel half cell when the two are contacted with the copper solution.

The several factors which aiect this oxidation potential are: concentration of the copper solution, both in total copper and in total halide;

temperature of the solution; relative amounts of copper in the cuprous states; and also the presence oi. other salts and substances. The efrect of temperature on oxidation potential is illustrated in Figure 1. It will be noted that the oxidation potenuai of a solution containing 45 grams cupric copper and 9B grams chloride per liter at 76F. is equal to that of a solution only 2/3 the concentration, but at 105 F. In Figure 2 is shown the rate of increase in the oxidation potential with increasing concentration of pure cupric chloride in the solution. In addition, the effect of increase in oxidation potential, as a result of increase of chloride concentration is illustrated. Figure 3 illustrates the eEect of small amounts of cuprous copper on the oxidation potentials of two copper solutions. l0

The examples in Table I illustrate the interrelatlon of some of these factors and indicate various ways in which a constant oxidation potential may be maintained.

Oxida- Copper Chlo. ou

proustion conc. conc. Temp. Example grams] grams] cc deg. F. lllli' liter liter vous 45 08 0.00050 06 aso 20 45 0s 0.00100 04 '380 34 74 0. 00030 9a 380 `4e 5a 0.00015 05 380 Examples l and 2 represent' solutions containing the same amounts of copper and chloride; the cuprous copper concentration has been allowed to increase so as to exactly counterbalance the change in oxidation potential which would normally result from lncrease'in temperature. 30 In Example 3 the copper and chloride concentrations are 3A those of the first two examples, the temperature is approximately the same as in the second example. In order that the oxidation potential remains constant, the cuprous copper 35 concentration was diminished. Example 4 illustrates the fact that the copperv to chloride ratio may be altered and the eiect compensated by varying the cuprous-cupric ratio. It is evident from the foregoing vthat the oxidation potential .M A

of the treating solution may be varied and controlled by either one or more of these factors.

In the sweetening of gasoline by means of copper halide solutions, unsatisfactory results may be obtained as a result of the treating solution possessing too high as well as toc low oxidation potentials. Copper chloride solutions of low oxidation potential are unsatisfactory for sweetening gasoline, in that cuprous mercaptides are left in the oil and produce what has heretofore been 50 referredto as a delayed doctor test. Therefore, a completely sweet product does not result when theoxidation potential of the treating solution is below the values given herein. @Many -gasolines contacted with copper chloride solution of high oxidation potential are entirely sweet to the doctor test, but possess undesirable properties, such as inferior color, and color and gum instability. It has been found, however, that an entirely satisfactory product may be obtained through suitable control of the sweetening solution strength throughout its cycle of sweetening and regenerating. By means of the factors al-u ready discussed the oxidation potential of the regenerated solution may be maintained below a maximum value; through limitation of the extent of spending, as by limiting the volume of gasoline per volume of treating solution, the solution strength may be kept above a minimum value.

In practice it has been found that the minimum value of the oxidation potential for satisfactory operation at average atmospheric temperature is 330 to 350 millivolts. While this is not an absolirte lower limit of possible operation, nevertheless operation at somewhat lower potentials necessitates further control and precaution not necessary above this limit. The maximum value of oxidation potential for satisfactory operation is completely dependent on the stock being treated. A gasoline containing only stablesaturateol hydrocarbons may be treated with a copper solution of 500-600 millivolts strength with very satisfactory results. But in treating relatively unstable, readily oxidized cracked gasolines, for example from West Texas crudes, solution strengths in excess of 430-450 millivolts are undesirable in that excessive color and gum instability result. In the treating of these less stable gasolines the limits of desirable values of oxidation potential are most narrow, and thus a controlled solution method is of greatest value; such controlled solution is, however, necessary for optimum treatment of any stools.

Examples of the sweetening of sour West cracked gasoline under satisfactory and unsatisn factory conditions are given. The charge stool?. was the same, containing approximately 0.02 per cent mercaptan sulfur. The gasoline after con=l tacting `with an equal volume of copper solution was separated from the copper solution and staz bilized by means of a sodium sulfide wash.; the colors of the resultant gasoline after treatment and at the end of a months storage are given in the table.

High oxi- Satifac- Low oxidodation tory tion potential operation potential Temperature F. 100 F. i F. Oxidation potential oi w n) Initial solution 451 i0! 368 b) Final solution.- 430 376 337 Doctor Sweet Sweet Trace son? Initial coloil (Saybolt 25 25 25 Color after treating 21 25 25 Color after 30 days storage in glass 12 z3 10 The difference between initial and final oxidation potentials is due to the increase in cuprous content of the copper solution as a result of the cupric copper reduced to cuprous copper during` the conversion of mercaptans to disuldes. This difference in oxidation potentials of the solution before and after the sweetenng step is dependent upon the amount of cuprous copper formed per unit volume; this in turn depends upon the souress (mercaptan content) of the gasoline and the ratio of copper solution to gasoline. Our improved process permits close control of the treating solution so that satisfactory operation is constantly secured. In the series of tests from which the above results are quoted, excellent operation was obtained in the range 415-360 millivolts.

The oxidation potential as here described may be used for the control of any copper sweetening solution, though ordinarily solutions containing appreciable copper ions and chloride and/or bromide ions will be those found most useful. Such solutions may be used to treat or sweeten any oils containing mercaptans, such oils being generally of the nature of kerosene, gasoline and other light petroleum distillates. solutions will contain halide ions in excess of the quantity necessary for the formation of the corresponding cupric salt.

Our process of sweetening and means of control is not to be limited by any example given by 'way of illustration, but to include all that come within the scope of the following claims, wherein it is to be understood. that the term oxidation potential is intended to include only the potential as-obtained in a manner equivalent to that herein described.

We claim:

ll. A process of sweetening mercaptan-loearing petroleum oil comprising contacting the oil with s. metallic halide solution havingan oxidation potential Within the range of 330 to 450 millivolts.

2. A process of sweetening mercaptan-bearing petroleum oil comprising contacting the oil with a treating solution consisting of a copper salt and a soluble chloride, said treating solution having an oxidation potential within the range of 33o to 45o millivolts.

3. it. process of sweetening mercaptan-bearing petroleum oil'co-mprising contacting the oil with a treating solution consisting of a copper salt and a soluble chloride. said treatingsolution having an oxidation potential within the range of 330 to 450 millivoits, separating the oil from the treating solution, contacting the oil with a stabilizing solution consisting of an alkaline sulfide, and separating the nished oil from the sulde solution.

t. In the process of sweetening petroleum distillates by contacting them with oxidizing solutions of copper bolides, the improvement which consists in maintaining the oxidation potential of the copper salt solution, while in contact with the said distillate, within the limits of 330 to lofi millivolts.

5. In the process of sweetening petroleum distillates by contacting them with oxidizing solutions of copper halides, the improvement which consists in maintaining the oxidation potential of the coppersalt solution, while in contact with the said distillates, within the limits of 360 to 415 millivolts.

JAMES A. REID. WALTER A. SCHULZE.

Usually the 

